Some of the factors involved in the development and functioning of retina, pigment epithelium (PE) and cornea are under investigation. In tissue culture, cyclic nucleotides and prostaglandins have been found to markedly influence the growth, morphology and pigmentation characteristics of PE cells. Cyclic nucleotides also affect the distribution of lysosomal enzymes in lysosomes of PE cells in vitro. Cyclic nucleotides may thus play a role in the development and normal functioning of the retina-PE unit. In other experiments, a specific, soluble low-molecular weight receptor for vitamin A alcohol (retinol) in the retina is under investigation. The receptor is different from the serum retinol-binding protein (RBP). No receptor has as yet been detected in soluble extracts of purified rod outer segments however. Two binding species are observed in PE cells, one similar to that of retina and one of higher molecular weight; specificity for retinyl esters is different for the two species. A similar low molecular weight receptor has been found in corneal epithelium and also in stroma. Specific binding of vitamin A acid (retinoic acid) is also observed in the retina and pigment epithelium of the chick embryo but not the cornea of several species. The receptor may be involved in the normal development and/or in vitamin A transport functions in ocular tissues.